Author Topic: Using Rigol DS815-TG for RS-485 analysis?  (Read 1014 times)

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Offline w3amd

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Using Rigol DS815-TG for RS-485 analysis?
« on: January 24, 2016, 12:25:27 PM »
Hi guys,

Would it be better to use a scope or spectrum analyzer for RS-485 analysis? I may have some noise problem but need to investigate. I'm getting a combination of additional unexpected data on the bus, alignment issues and CRC errors. Some times an extra character appears in front of the data packet.

If it would be the spectrum and the spectrum expects 50 ohms load what would I need to add externally to measure with the spectrum.

Load on the ends of each RS-485 side should be about 120 ohms so this in parallel I expect would be half. However, currently the line lead on the RS-485 bus is less than a meter long so it isn't terminated at either end.

Cheers,
John
« Last Edit: January 24, 2016, 12:27:04 PM by w3amd »
 

Offline TheSteve

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Re: Using Rigol DS815-TG for RS-485 analysis?
« Reply #1 on: January 24, 2016, 04:52:12 PM »
No idea how you'd use a spectrum analyzer for that unless you're experiencing some RF interference. A scope is your best bet, especially if it has a serial decoder built into it.
VE7FM
 

Offline w3amd

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Re: Using Rigol DS815-TG for RS-485 analysis?
« Reply #2 on: January 25, 2016, 07:20:31 AM »
Hi Steve,

Thanks for your response. I was going to look for the offending frequency. I have further development on this from testing so I'll add a post because the subject is now different.

John
 

Offline georges80

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Re: Using Rigol DS815-TG for RS-485 analysis?
« Reply #3 on: January 25, 2016, 08:01:07 AM »
Scope. If the interference is large enough to affect the differential nature of RS485 you should EASILY be able to see it with a scope. With 2 channels you can look at the input and output of the RS485 transceiver.

cheers,
george.
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Offline w3amd

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Re: Using Rigol DS815-TG for RS-485 analysis?
« Reply #4 on: January 25, 2016, 08:02:59 AM »
Thanks George,

If I can get up the hill tomorrow to get into the office I'll give it a look. We got a meter here on the East Coast yesterday.

John
 


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